Our preliminary investigations have demonstrated that the antibiotic edeine A1 directly inhibits bacterial DNA synthesis in vivo and in vitro. It does not inhibit the reaction catalized by DNA polymerase I from E. coli and, at bacteriostatic concentrations, it does not inhibit the growth of some DNA-containing coliphages. The effect of edeine A1 is specific, i.e., it is readily distinguishable from polycationic effects related to the nature of the antibiotic. Our research is aimed at determining the step(s) at which edeine A1 inhibits bacterial DNA synthesis. We will attempt to distinguish rigorously between the effect of edeine A1 on the initiation of replication and on the elongation of the initiated chromosome by differential labeling of the origin and terminus of the chromosome in E. coli auxotrophs. We will also attempt to distinguish between the effect of edeine A1 on repair and replicative synthesis by assaying the level of repair synthesis in UV-irradiated E. coli cells after a shift to a "heavy" medium. With this evidence we will proceed to narrow down on the edeine-sensitive target. We shall look for E. coli mutants resistant to edeine with respect to DNA synthesis. We shall attempt to locate the action of edeine A1 within the cell using electron microscope techniques coupled with C14-edeine binding experiments. We intend to start experiments with eukaryotic systems using the established cell line known as BSC-1 which allows the growth of the oncogenic virus SV 40. If successful, our work should enhance the current understanding of the replication of DNA in bacteria. Past experience indicates that specific antibiotic inhibitors become invaluable tools in biosynthetic studies as soon as their mechanism of action is known.